This invention relates to a kiln construction and the method of firing kilns or the like. The invention is applicable to kilns (ceramic furnaces) or metallurgical furnaces.
In the firing of kilns it is essential that the heating be controlled so that the ware may be heated from room temperature to red heat and cooled down at a rate that will not destroy the ware. It is also desirable that the temperature gradient within the ware be maintained as low as possible as the ware is heated and cooled. If the temperature of the surface of the ware is changed too rapidly, a high temperature gradient is produced within the ware which may result in a defective product. Also it is desirable that the ware be heated and cooled uniformly throughout its surface area. A further requirement of good kiln operation is to maintain as close to a constant temperature as possible during the holding period.
One method of attempting to maintain a uniform holding temperature in the past has been to turn burners on and off rapidly with burners operating at a high velocity for a short duration and then turned down or off until heat demand is again required. This pulse technology, while an improvement over existing systems in many applications, still produced an unsatisfactory level of temperature excursions.
Batch firing of ceramic and other materials often requires a wide range of burner operation. In some processes, it is required to maintain temperatures of close to 100 degrees centigrade, while in others a temperature range in excess of 1700 degrees centigrade is required.
One other approach taken in the past was to use excess air type burners so that the low temperature requirements could be met. This approach consumes extra fuel, requires large exhaust fans to exhaust combustion air from the kiln and, to minimize air pollution, requires reheating of the exhaust by-products.
The pulse technology, as mentioned above, eliminates some of these problems, but can have high temperature excursions. However, a rapid pulse system, with short pulse durations, as low as one second, combined with a secondary burner with a constant low firing rate in the range of 1000 BTU's per hour and a main pulsed burner with the capacity of firing as high as 1,000,000 to 1,500,000 BTU's per hour has the capability of maintaining both the low and high temperature ranges with minimal temperature excursions.
With the foregoing in mind, it is therefore a principal object of the present invention to provide a pulse system for operating burners in a kiln to maintain holding or soaking temperatures within a preset narrow range of temperature with limited acceptable variations over a long holding period.
A further object of the present invention is to provide a pulse system for operating burners in a kiln in which burners throughout the length of the kiln may be individually controlled and pulsed sequentially throughout the length of the kiln to reduce pressure spikes in the kiln and maintain a uniform temperature within the kiln.
Another object of the present invention is to provide a novel burner for a kiln pulse system utilizing a two stage nozzle in which the first stage is constantly on during operation of the kiln with a low burn rate in the range of about 1000 BTU/hour and a second stage which can be pulsed on for a duration of approximately one second at a burn rate of anywhere from 20,000 to 1,500,000 BTU/hour and then off for variable periods of from one to ten or more seconds depending on the temperature requirements.
A still further object of the present invention is to provide a burner for a kiln pulse system which is durable, efficient and reliable.
Still a further object of the present invention is to provide a pulse system for operating a kiln in which multiple burners are individually controlled in response to feedback from multiple thermocouples in the kiln by a programmable controller responsive to measured conditions within the kiln.